Recently, micro-focus X-Ray (micro-focus:<100 um×100 um) is developed quickly in medical treatment, health and aerospace areas. The research and development of X-Ray devices with small focus and high power arouses researchers' attention from different technical areas. The key technology of micro-focus X-Ray application is a source of micro-focus X-Ray: cathode of micro-area X-Ray tube. However, with the fast improvement of resolution and power of tube electron, the needs of small size and high power cathode become urgent, and the research and development of cathodes with high dimensional accuracy and high current emission is more and more important.
Scandia-doped dispenser cathode is the highest emission cathode. However, the preparation of this kind of cathode is complicated since secondary deformation is caused by molten salt, the sintering process can't be finished on one time. It has poor repeatability and is not satisfied with the desirable cathode requirement of micro-area X-Ray tubes. The formation of pressed Scandia-doped dispenser cathode can be finished on one time, but active materials distribute heterogeneous, resulting in poor structure homogeneity. Further, high emission performance can't be reached. In normal cathode sintering, the heating rate of the traditional sintering furnace is 5-10° C./min, and it takes 350-400 min to finish the whole process. Thus, under conventional methods, a lot of energy is wasted and, a long cooling time of sintering process leads to grain growth while repeatability is poor.
Microwave sintering is a new sintering technology with immediacy such that materials are heated as long as there has a microwave radiation. When microwave radiation is stopped, a heating process is stopped immediately. Thus, the fast heating can be realized, and energy transforming rate of the microwave is high, and heating rate can be reached in 40-50° C./min and easier to reach 1600° C. Since the heating and cooling process is fast, ultrafine grain materials are obtained. Under microwave sintering, grain growth is restrained, the microstructure of materials is improved significantly, the mechanical property of fine grain is excellent, and the contraction ratio of microwave sintering is reduced significantly compare with normal sintering. Further, the vertical shrinkage and horizontal shrinkage of this sample are only one third as much as normal sintering samples.
In conclusion, there is a need for finding an energy saving and one-time forming sintering method with fast heating and cooling rate to obtain a cathode with homogeneous structure and fine grain size. It is meaningful for improving the performance of micro-focus X-Ray and developing of terahertz vacuum electronic devices.